Lead battery welding method and apparatus

ABSTRACT

A welding method for fusing lead components together in a leadcontaining electrochemical cell is disclosed together with apparatus for carrying out the method. The method includes forming an ingot-like mold around the lead components to be welded, the walls of the mold being comprised of a material having a high softening point, good thermal conductivity and arcerosion resistance. Arc welding of the components utilizing an inert-gas-shield nonconsumable electrode, e.g. tungsten, is accomplished by passing the electrode over a weldable surface formed by the lead components in an oscillating path at a controlled speed and welding current to permit the lead components to melt and flow into the ingot-like mold while simultaneously controlling heat transfer through the adjacent mold walls. The resultant weld is of low internal impedance and is relatively thick for increased oxidation and corrosion resistance during operation of the battery.

United States Patent 1191 1111 3,806,696 Young et al. Apr. 23, 1974 154]LEAD BATTERY WELDING METHOD AND APPARATUS Primary Examiner-C. L.Albritton Assistant Examiner-George A. Montanye [75] Inventors RolandDonald Attorney, Agent, or Firm-Curtis H. Castleman, .lr.; H. H.McClelland, Littleton, Edward w Ober Jr Ra mend H k Wolcott, Denver, allof Colo. y n

[73] Assignee: The Gates Rubber Company, [57] ABSTRACT Denver, Colo. i Awelding method for fusing lead components to- 1 1 Filedl g- 1972 getherin a lead-containing electrochemical cell is dis- [211 Appl No: 277,946closed together with apparatus for carrying out the method. The methodincludes forming an ingot-like mold around the lead components to bewelded, the

[ 219/137, 136/135 S, 136/176, walls of the mold being comprised of amaterial having 2 9/ 5, 219/121 219/161 a high softening point, goodthermal conductivity and [51] Int. Cl B23k 9/00 ion esista ce. Arcwelding of the components [58] Field Of Searc utilizing aninert-gas-shield nonconsumable electrode,

219/7 136/176, 1 5, 135 e.g. tungsten, is accomplished by passing theelectrode over a weldable surface formed by the lead compo- 1 1 IReferences Cited 7 nents in an oscillating path at a controlled speedand UNITED STATES PATENTS welding current. to permit the lead componentsto melt 3,589,948 6/1971 Adams 136 176 and the ingot'like mold WhileSimultaneously 3,493,035 2/1970 Tiegel et al. 136/176 Controlling heattransfer through the adjacent mold 1,807,477 5 1931 Hume 219/137 walls.The esultant weld is of low internal im edance 3,646,309 2/1972 Smith,Jr. et al. 219/130 and is relatively thick for increased oxidation andcor- 3,646,31 1 2/1972 Cameron et al. 219/131 rosion fesistance duringoperation of the battery 2,340,796 2/1944 Chyle 219/137 2,920,133 1 1960Greene 219 123 13 Claims, 3 Drawing Figures LEAD BATTERY WELDING METHODAND APPARATUS I BACKGROUND OF THE INVENTION This invention relates toelectrochemical cells containing weldable lead components andparticularly to method and apparatus for effectively welding thin leadbattery components together using a modified are casting technique.

Conventionally, various types of lead-containing electrochemical cellssuch as storage batteries, standby batteries, and sealedmaintenance-free lead-acid cells have employed the burning process orgas welding process to join lead components parts of the cell. Suchcomponent parts may include the current collector or plate tabs and leadpost terminals or bus bar, for instance, to which a fused connection isrequired for conducting current to the output terminals of the cell.While the buring process has been generally effective for fusingrelatively large lead parts together, the trend toward miniaturizationof various types of lead acid batteries, such as a D size of theaforementioned sealed maintenance-free variety has created a need fora-welding process for application to relatively thin or small leadcomponents. For instance, the current collector tabs in D or X sizesealed maintenance-free batteries may be of an expanded mesh of only20-4O mils in thickness. A further problem is that the resultant weldbetween such thin collector tabs and a lead post, for instance, shouldbe relatively thick to reduce the probability of an open-circuitoccurring as a result of an oxidation or eating away of the weld jointduring cell operation and storage.

The traditional burning procss as well-as other welding processes oftenemploy a filler rod and/or flux which contribute to the foramtion ofslag which is conducive to corrosion of the lead parts being welded.Further disadvantages of the burning process are that it is relativelyslow, and due to its inherent inconsistency requires the attendance ofskilled operators for its implementation.

Among the pertinent prior art references include patents from unitedStates Patent Office Classifications Class 219, Sub-classes 137 and 161and Class 136, Subclasses 13 and 14. U.S. Pat. No. 540,076 to Silveydiscloses a process for welding lead parts in a battery using a carbonarc welding process.

The present invention has as its primary object to overcome thedrawbacks of the prior art, providing an economical process andapparatus therefore which allow uniform welding of relatively small leadparts in a lead-containing electrochemical cell, the weld produced beingof low internal impedance, e.g. less than one milliohm, of highcorrosion resistance, relatively thick in transverse section, andintroduced by a rapid process requiring relatively unskilled attendants.

SUMMARY OF THE INVENTION Accordingly, in general the method of thepresent invention is basically an arc welding process using aninert-gas-shielded nonconsumable electrode. After the lead componentsare brought into close proximity to form a weldable surface, the surfaceis surrounded with an ingot-like mold whose walls are comprised of amaterial having a high softening point, good thermal conductivity andarc-erosion resistance. The welding electrode is passed over the weldingsurface in a back and forth oscillating path to produce a wide, smooth,thick weld bead having a generally pore free appearance. The weldingcurrent and oscillation speed and amplitude of the welding head arechosen to cause the lead components being welded to flow together andessentially fill the ingot-like mold. The mold in turn rapidly causesthe flowing lead to solidify from its periphery inwardly by heattransfer through the walls of the mold.

The apparatus for carrying out the method includes a welding table, acell assembly holding fixture, the cell having exposed lead parts inclose proximity to form a weldable surface, ingot-like mold means formedin part preferably by a pair of opposed movable jaws, a welding torchmovable with respect to the weldable surface, means for producing awelding arc utilizing an inert-gas-shield nonconsumable electrode, andmeans for oscillating the torch across the weldable surface.

BRIEF DESCRIPTION OF THE DRAWING The invention will be more particularlydescribed with reference to the accompanying drawings, in which:

FIG. 1 depicts a plan view ofthe main portions of the apparatus forcarrying out the method of the present invention;

FIG. 2 is a front elevational view ofthe apparatus of FIG. 1 showing thelead post-locator in the withdrawn position; and

FIG. 3 is an expanded view of the ingot-likemold arrangement andweldable surface.

PREFERRED EMBODIMENTS OF THE INVENTION Referring to the Figures, thereis shown a welding table 10 comprised of a main stationary section 12and a rear section 14 movable toward and away from section 12 alongguides 16 asindicated. A torch welding head 18 is pivotally andoscillatably mounted (not shown) on rear carriage 14. The welding head18 is a conventional inert-gas-shielded arc wleding unit comprising anonconsumable electrode axially disposed within the electrode headportion20, the electrode preferably being composed of tungsten or analloy thereof. The shielding gas, e.g. argon or helium is deliveredthrough line 22 and blown throughan annular opening concentric with theaforementioned electrode within head portion 20 and expelled to form aninertgas shield non-oxidizing atmosphere to protect the weldable surfacefrom local contamination and oxidation. Small percentages of hydrogen orother reducing gas may be admixed with the primary shielding gas.

Welding table 12 contains a work piece receiving slot 22 havingjuxtaposed parallel guides 24*for slidably receiving cell assemblyholding fixture 26. This fixture 26 has axially positioned therein anelectrochemical cellpack subassembly 28. The cellpack shown is comprisedof spirally wound positive andnegative lead plates and interleavedporous absorbent separator material. Obviously various other types andconfigurations of cell subassemblies, such as a parallel stackedarrangement, would be amenable to the welding process and apparatus ofthe present invention.

The electrode plates of the cell of subassembly 28 are by way of exampleformed of an expanded mesh, lead foil or other suitable grid substrateupon which-is affixed a uniform bonded layer of electrochemically activelead paste. In a convenient manner the grid substrate has a plurality ofintegral collector tab extensions 30. As shown, each individual platecontains a plurality (four shown) of upstanding collector tabs exitingfrom one side of an end of the cellpack in close relationship to oneanother. On the opposite side of the cellpack are also shown fourextending collector tabs 30 for the corresponding opposite polarityplate shown already welded to lead post 32 according to the presentinventron.

It will be noted that prior to the welding operation the collector tabs30 are brought into close proximity to lead post 32 such as by crimpingthe same together. Other prewelding operations such as thorough cleaningor chemical conditioning may be employed. The finished subassembly 28with tabs welded to the posts may be conveniently enveloped in a plasticliner and top, and connections made from the lead posts through theplastic top to the positive and negative terminals of the battery, suchas taught in commonly assigned McClelland et al. U.S. Pat. No.3,704,173.

Preparatory to welding, the lead post 32 is placed in position with theaid of connector post locator 34 having pivotally connected arm 36, anapertured post receiving portion 38 and a vacuum bonnet with vacuum line40 for retaining the post 32. FIG. 2 shows the locator 34 and post 32 inthe ready position, while FIG. 1 shows the locator and post in thelocated, pre-weld position. After the post is located, locator 34 iswithdrawn to the rightmost position shown in FIG. 2 but without post 32.In this position the arm 36 is conveniently in conductive relationshipwith a safety micro-switch through spring 42 so that the welding torch18 remains off until the switch has been closed to prevent the torchfrom hitting the locator during a welding pass.

According to a preferred embodiment of the invention, a pair of opposedmovable jaws 44 and 46, shown in the ready position in FIG. 1 areoperatively closed about lead collector tabs 30 and interposed lead post32 prior to removal of locator 34. An ingot-like mold is formed as aresult as shown in FIG. 3. The engagement of jaws 44 and 46 may beactuated in any convenient manner, such as hydraulically orpneumatically. As the jaws are brought together, each pair of collectortabs straddling post 32 are drawn inwardly and in close proximity(preferably in intimate contact) to the post 32 to form, together withthe forward portion 48 of the post 32 what will be defined as a weldablesurface. It will be noted that the mouth portions 50 and 52 of each ofthe jaws form upstanding projections or walls which define an edifice orboundary around a substantial portion of the weldable surface. Theingot-like mold walls are further defined by mid-portion 54 of the leadpost which nearly, if not entirely, bridges and dams the remaining gapbetween mouth portions 50 and 52 of the mold.

The jaws 44 and 46 are of a material which has adequate electricalconductivity, a softening point well above that of lead, good thermalconductivity (preferably at least about 0.12 cal/cm /cm/ C/sec) andrefractory enough to be resistant to erosion caused by the welding arcwhich subsequently traverses the jaws during the welding operation. Itis also important that the jaws exhibit a low creep rate at the arcwelding temperature. At the present time, jaws 44 and 46 are preferablymade of substantially pure tungsten or a suitable alloy thereof (e.g. 2percent thorium) since these materials best satisfy the above enumeratedparameters, although it will be appreciated that other materials such astitanium, tantalum, carbon, steel or copper are generally satisfactoryfor the intended purpose. Copper cooled internally with circulatingwater is satisfactory, as well as copper or other material carryingsurface layer of tungsten. One or both of the jaws may be used as thecounter-electrode for the welding operation, either as the positive ornegative electrode.

In operation of the invention, the cell assembly holding fixture 26 isinserted into the welding table 12 on guides 24 and lead post 32 locatedbetween one set of collector tabs 30, which may be individually crimpedtogether for improved contact as shown in FIG. 2. Jaws 44 and 46 arethen actuated to form the ingot-like mold and intimate contact with themarginal portion of the welding surface as shown in FIG. 3. The locator34 is then withdrawn.

At this point the welding arc is struck, preferably utilizing a weldinggenerator and control panel, commercially obtainable. It has been foundquite desirable according to the invention to employ a type of hot startshort of the welding surface. As shown in FIG. 1, the torch head 20 ispreferably started up at a relatively high current, e.g. 5O amperes,while still being spaced a distance away from the weldable surface. Thetorch 18 is also set into oscillatory motion so that electrode head 20oscillates back and forth with amplitude A in a plane preferably normalto the horizontal. To effect welding, the control panel current is setto a desired current, well below the hot start current, e.g. 15 amperes,and carriage 14 made to move toward weld table 12 to produce a resultantoscillatory welding path over the weldable surface schematicallyrepresented by curve P.

As with the welding current and height of the welding electrode abovethe weldable surface, the rectilinear speed of carriage 14, theoscillation speed of the welding head 20, and the oscillation amplitudeA are variably selected to produce sufficient distributed heat over theweldable surface to cause the lead component parts to freely flow intoat least a substantial portion of the ingot-like mold. Oscillationspeeds of preferably from about 60 to about 2,400 and more preferablyfrom about 400 to about 1,200 strokes per minute have given goodresults. The amplitude of oscillation will in general be variable asdesired, although it is preferred that the amplitude be at least asgreat as needed to cover the approximate width of the weldable surface.A resultant wide, smooth and relatively thick weld bead is obtainedhaving a substantially pore free appearance. While a generallysinusoidal welding path P has been illustrated, other types ofoscillating paths such as a triangular wave form would be satisfactory.Different means for producing the oscillating path could also beemployed, such as by subjecting a stationary welding head to theinfluence of a changing magnetic field to thereby cause the desired arcoscillation.

In any event, the overall welding speed should be at least as great asis necessary to avoid burning the lead components.

A typical finished weld bead is shown at 56. While some prior arcwelding processes have employed a type of related puddling technique,significant benefits are obtained from the method of the presentinvention by virtue of the dual role played by jaws 44 and 46.

Namely, the walls of the jaws 44 and 46 serve to physically contain andshape the forming weld bead, together with very importantly acting as acontrollable heat sink of very good thermal conductivity. The walls actto rapidly cause the leading edges or peripheral extensions of theflowing lead to cool inwardly toward the centroid of the weldablesurface. In this manner, a relatively thick ingot-like weld bead isobtained with a minimum of effort and equipment.

It will be noted from FIG. 3 as the welding head traverses the weldablesurface that portion of the weldable surface which has not been heatedappreciably by the tungsen arc will remain unmelted and tend to functionas a wall or barrier for the ingot-like mold. For this reason, it ispreferred to terminate the arc path at the approximate longitudinal endE of the collector tabs to prevent melting the mid-portion 54 of thelead post which acts as one of the containing walls of the mold.

After the weld has been made, it is unnecessary to employ a peening orother operation to remove slag inasmuch as no flux or filler rod hasbeen used for which slag would be created.

After the first weld has been made, holding fixture 26 may be removedfrom the welding table and rotated 180 and reinserted into the tablepreparatory to making the other weld.

It should be understood that the invention is capable of a variety ofmodifications and variations which will become apparent to those skilledin the art upon reading the specification. Such modifications areintended to be encompassed within the scope of the invention as definedby the appended claims. For instance, while the welding apparatus hasbeen described with reference to a moving electrode torch l8, and astationary welding table 12, the reverse would be applicable so long asthe relative required oscillatory motion is maintained.

What is claimed is:

1. A method for welding together thin lead current collector tabs to alead post of high heat capacity relative to the collector tab allcontained within a lead-acid electrochemical cell, without the use offlux to produce a low impedance, intra-cell corrosion resistant weld,comprising:

a. bringing the thin lead current collector tab(s) into close relativeproximity to the lead post to form a weldable surface;

b. forming an ingot-like mold at least substantially surrounding andforming walls about the periphery of said weldable surface, said wallscomprised of a metal having a softening point well about the soft- 6ening point of lead, good thermal conductivity, and refractory enough tobe resistant to erosion caused by welding arcs;

c. arc welding said lead components utilizing an inert-gas-shieldednonconsumable electrode by passing the electrode over said weldablesurface in an oscillating path at a welding current, speed andoscillation amplitude sufiicient to cause said lead components to flowtogether, the flow being contained by the walls of the ingot-like mold;and

d. rapidly causing said flow to solidify from its periphery inwardly byheat transfer through said walls.

2. The method of claim 1 wherein the current collector tabs having athickness in the range of about 20-40 mils.

3. The method of claim 1 wherein said nonconsumable electrode consistsessentially of tungsten or an alloy thereof.

4. The method of claim 1 wherein the walls of said ingot-like mold areformed essentially of tungsten.

5. The method of claim 1 wherein said arc welding step is conducted inan essentially non-oxidizing atmosphere.

6. The method of claim 1 wherein said oscillation speed is from about 60to about 2,400 strokes per minute.

7. The method of claim 1 wherein the speed of oscillation is from about400-1 ,200 strokes per minute.

8. The method of claim 1 wherein the impedance of the weld is less thanone milliohm.

9. The method of claim 1 wherein said weldable surface is defined by alength in the longitudinal direction of the welding path, and a width,the amplitude of said welding path corresponding substantially to saidwidth of the weldable surface.

10. The method of claim 9 wherein said oscillating path is substantiallysinusoidal.

11. The method of claim 1 wherein the metal walls have a thermalconductivity of at least about 0.12

high as to cause burning of the flowing lead.

1. A method for welding together thin lead current collector tabs to alead post of high heat capacity relative to the collector tab allcontained within a lead-acid electrochemical cell, without the use offlux to produce a low impedance, intracell corrosion resistant weld,comprising: a. bringing the thin lead current collector tab(s) intoclose relative proximity to the lead post to form a weldable surface; b.forming an ingot-like mold at least substantially surrounding andforming walls about the periphery of said weldable surface, said wallscomprised of a metal having a softening point well about the softeningpoint of lead, good thermal conductivity, and refractory enough to beresistant to erosion caused by welding arcs; c. arc welding said leadcomponents utilizing an inert-gasshielded nonconsumable electrode bypassing the electrode over said weldable surface in an oscillating pathat a welding current, speed and oscillation amplitude sufficient tocause said lead components to flow together, the flow being contained bythe walls of the ingot-like mold; and d. rapidly causing said flow tosolidify from its periphery inwardly by heat transfer through saidwalls.
 2. The method of claim 1 wherein the current collector tabshaving a thickness in the range of about 20-40 mils.
 3. The method ofclaim 1 wherein said nonconsumable electrode consists essentially oftungsten or an alloy thereof.
 4. The method of claim 1 wherein the wallsof said ingot-like mold are formed essentially of tungsten.
 5. Themethod of claim 1 wherein said arc welding step is conducted in anessentially non-oxidizing atmosphere.
 6. The method of claim 1 whereinsaid oscillation speed is from about 60 to about 2,400 strokes perminute.
 7. The method of claim 1 wherein the speed of oscillation isfrom about 400-1,200 strokes per minute.
 8. The method of claim 1wherein the impedance of the weld is less than one milliohm.
 9. Themethod of claim 1 wherein said weldable surface is defined by a lengthin the longitudinal direction of the welding path, and a width, theamplitude of said welding path corresponding substantially to said widthof the weldable surface.
 10. The method of claim 9 wherein saidoscillating path is substantially sinusoidal.
 11. The method of claim 1wherein the metal walls have a thermal conductivity of at least about0.12 cal/cm2/cm/* C/sec.
 12. The method of claim 11 wherein said arcwelding step is accomplished by initially starting the arc at arelatively high current short of said weldable surface, followed bylowering the welding current well below the start-up current value, andthen passing the electrode ovEr said weldable surface at the reducedcurrent.
 13. The method of claim 12 wherein the lower current value issufficient to melt the lead components and cause them to readily flowwithin the mold, but not so high as to cause burning of the flowinglead.